Monaural communication at a constant bit rate is currently mainstream in speech communication such as calls using mobile telephones in a mobile communication system. However, if transmission is realized at much higher bit rates as with the fourth-generation mobile communication system in the future, it is expected that speech communication using stereo signals having higher fidelity will be widely available.
One of coding methods for stereo speech signals is disclosed in Non-Patent Document 1. This coding method predicts one channel signally from the other channel signal x using following equation 1 and encodes such prediction parameter ak and d that minimize prediction errors. Here, ak is a Kth-order prediction coefficient and d is a time difference between the two channel signals.
                    [        1        ]                                                                      y          ⁡                      (            n            )                          =                              ∑                          k              =              0                        K                    ⁢                                          ⁢                                    a              k                        ·                          x              ⁡                              (                                  n                  -                  d                  -                  k                                )                                                                        (                  Equation          ⁢                                          ⁢          1                )            Non-Patent Document 1: Hendrik Fuchs, “Improving Joint Stereo Audio Coding by Adaptive Inter-Channel Prediction,” Applications of Signal Processing to Audio and Acoustics, Final Program and Paper Summaries, 1993 IEEE Workshop on 17-20 Oct. 1993, Page(s) 39-42.